Lead-in conductor



Dec. 15, 1936 EXPANSION OFA MD IMETER LONG IN MILL/ME TE RS E. W.STEVENS LEAD- IN CONDUCTOR Filed Jan. 14, 1955 COPPER V 7' PLATINUM LAMPGLASS COPPER CLAD NIGKEL STEEL WIRE TE MPE RA TURE Patented Dec. 15,1936 UNITED STATES PATENT OFFICE LEAD-1N CONDUCTOR Elbridge W. Stevens,Baltimore, Md.

Application January 14, 1935, Serial No. 1,811

1 Claim. (Cl. 176-38) My invention relates to lead-in conductors forincandescent lamps, radio tubes, mercury rectifiers, and the like, andit consists in the combinations, constructions and arrangements hereindescribed and claimed.

An object of my invention is to provide a leadin conductor which can bequickly fabricated so as to have substantially the same coefilcient ofexpansion as that of the glass or similar envelope in which it issealed.

A further object of the invention is to provide a lead-in conductorwhich can be fabricated while in a cold state and .which does notnecessitate the welding of the various materials which enter into thecomposition of the conductor.

Other objects and advantages will appear in the following specification,and the novel features of the invention will be particularly pointed outin the appended claim.

My invention is illustrated in the accompanying drawing forming part ofthis application, in which:

Figure 1 is a graph showing the rate of expansion of copper-clad nickelsteel-wire, ordinarily lamp glass, platinum and copper.

Figure 2 is a cross section of the lead-in wire, and,

Figure 3 is a longitudinal sectional view showing one end of the lead-inwire.

In carrying out my invention I make use of a tube of copper, such asthat shown at l in the drawing. The copper of which the tube is formedis deoxidized by a treatment with phosphorus and is substantially 99.9pure. The diameter of the tube and the thickness of the walls thereofwould vary according to the uses to which the lead wire is to be put.For instance, with a finished lead-in conductor of twentythousandths ofan inch outside diameter, I may take a copper tube having an outsidediameter of- $102" 62.3% PbO 22.4 NazO 7.0 K20 8.3

I may use as a filler such materials as manganese oxide, MnaOa,comminuted carbon, plaster of Paris, china clay, fuller's earth,graphite or the like. These materials have different coeflicients ofexpansion, and thus materials are used which when used with the coppersheath will 5 most nearly approximate the coefiicient of expansion ofthe glass to which the lead-in wire is being sealed. As an example, Imay fill the tube with a mixture comprising 90% of manganese oxide, 5%graphite and 5% plaster of Paris.

The filling material of course is in the form of powder and the size ofthe grains may vary, but I usually prefer to use grains of difierentsizes, for instance, grains of one-hundred sixty to onehundred eightymesh of the manganese oxide, 15 with grains as small as four-hundredmesh of the other ingredients, although the particular size of thegrains is not necessarily essential.

The filling material shown at 2 in the drawing is first thoroughly mixedand then tightly packed 20 in the tube. The end of the tube may then beclosed as by soldering, as shown at 3 in Fig. 3, or by fusing the endsof the tube, or in any other suitable manner and the lead-in conductoris then fabricated by swaging, in a swaging device, 5 which device isordinary and forms no part of the present invention.

I find, however, that a better product is effected by the use of aswaging machine than by attempting to draw out the tube. In the swagingma- 0 chine the forces acting inwardly or toward the center form a moreuniform product so that eventually a lead-in conductor oftwenty-thousandths of an inch in diameter can be made in which thevarious sections of the tube will be 35 found to be substantiallyhomogeneous.

The example given above has been found to give substantially the samecoeflicient of expansion as that of the ordinary glass in anelectriclight bulb.

In forming the sealing operation I prefer to apply a coating to thelead-in conductor, preferably zinc borate, although other forms ofborate are useful. Zinc borate, however, is non-hygroscopic and whenused at a sealing temperature, 45 tends to form a cementing materialwhich is highly efiicient because of its tendency not only to cling tothe copper, but because it partakes somewhat of the nature of the glassitself, and virtually formsa part thereof at the fusing temperature. 50

A lead-in wire formed in accordance with this invention has severaladvantages. It can be quickly prepared with a choice of filling materialwhich experience has shown will give the finished lead-in conductorsubstantially the same coefiicient as that of the glass, as stated. Thefilling material being under pressure in the copper sheath, gives aconductor which is not subject to collapse with consequent withdrawalfrom the edges of the glass, as happens with those conductors mademerely of shells or copper or the like.

Furthermore the lead-in conductor is one which is not easily mutilatedbecause the core is under compression as distinguished fromhollow.leadin wires. At the same time the conductor has a greater degreeof flexibility than other lead-in conductors such for instance as thenickel steel wire mentioned above.

One of the main features of the invention is the fact that the core ismade of materials all having a higher fusing point than the temperatureof the sealing. The physical characteristics therefore of the materialsof the core are not changed and are comparatively unaffected by thesealing heat. For this reason the seal when cold does not have thetendency to open up with consequent leakage of the gas, as is the casewith certain of the lead-in conductors heretofore referred to.

While the example given above is a preferred form for glass of a certainquality it is obvious that other ingredients among those named abovemight be used for the core and that the sheath of copper might be moreor less any thickness to suit varying conditions of use.

I claim:-

A lead-in conductor comprising an exterior tube of deoxidized copper anda filler comprising a mixture of manganese oxide, graphite and plasterof Paris.

ELBRIDGE W. STEVENS.

